Conventionally, with an object to prevent forgery, magnetic ink including magnetic material has been used to perform printing on paper sheets such as checks, merchandise coupons, etc. The magnetic inks include inks of different magnitudes of coercive force, such as a hard magnetic ink and a soft magnetic ink. If the magnetic inks used to perform printing on a paper sheet can be precisely detected, it can be decided whether the paper sheet is authentic.
An example of a device that detects magnetic ink on paper sheets has been disclosed in Patent Document 1. The magnetic property detection apparatus disclosed in Patent Document 1 generates a magnetic field directed perpendicularly to a transport path of a paper sheet and detects magnetism of the paper sheet when the paper sheet passes through the magnetic field. In this apparatus, an upper unit and a lower unit are arranged above and below the transport path of the paper sheet. Two magnets coupled via a yoke are accommodated in the inside of the upper unit and the lower unit, respectively, and these magnets generate a magnetic field vertically across the transport path. Because the magnetic field is generated at the location of the sensor that detects the magnetism of the paper sheet in a direction perpendicular to the direction of transport of the paper sheet, i.e., in a direction in which the magnetic force is vertically transmitted through the paper sheet, the magnetic ink used to perform printing on the paper sheet can be detected with a high precision.